A flat panel detector has been developed in recent year which has a sensor array which uses as a material an amorphous silicon deposited and formed on an insulating substrate such as glass and has a two-dimensional arrangement of pixels composed of photoelectric conversion elements and switching elements and has been applied to a medical X-ray imaging apparatus.
The X-ray imaging apparatus using such a flat panel detector is described in Japanese Patent Application Laid-Open No. H08-299316, for example. An X-ray imaging system including a conventional X-ray imaging apparatus disclosed in Japanese Patent Application Laid-Open No. H08-299316 is described with reference to a drawing.
FIG. 20 is a schematic diagram of a conventional X-ray imaging system.
The conventional X-ray imaging system illustrated in FIG. 20 includes an X-ray generation apparatus 200, a flat panel detector 401, a signal processing unit 402, a display unit 403, a light deriving unit 404, a photo detector 405, an amplifier 406 and an X-ray condition controller 407.
In the conventional X-ray imaging system illustrated in FIG. 20, an object 300 is irradiated with X-rays 201 from the X-ray generation apparatus 200 and the X-rays 201 penetrating through the object 300 are incident on the flat panel detector (FPD) 401. An image signal detected by the flat panel detector 401 is processed in the signal processing unit 402 and then the image based on the image signal is displayed on the display unit 403.
The light deriving unit 404 detects the dosage of the X-rays penetrating through the flat panel detector 401. Information on the dosage of the X-rays detected by the light deriving unit 404 is sent to the X-ray condition controller 407 through the photo detector 405 and the amplifier 406. The X-ray condition controller 407 controls the X-ray irradiation condition of the X-ray generation apparatus 200 so that the dosage of the X-rays penetrating through the flat panel detector 401 is kept constant.
Japanese Patent Application Laid-Open No. H08-299316 describes that an image intensifier (II) and the optical system are provided instead of the flat panel detector to control the X-ray irradiation condition of the X-ray generation apparatus so that the dosage of the X-rays is kept constant, as is the case with the above.
U.S. Pat. No. 6,163,029 describes a technique that the characteristic of a processing circuit at a front stage is changed so as to fall within the dynamic range of the processing circuit at the front stage according to the X-ray irradiation condition.